title: Proton-bound dimers of 1-methylcytosine and its derivatives: vibrational and NMR spectroscopy.
abstract: Vibrational spectroscopy and NMR demonstrate that the proton-bound dimer of 1-methylcytosine, 1, has an unsymmetrical structure at room temperature. In the gas phase, investigation of isolated homodimer 1 reveals five fundamental NH vibrations by IR Multiple Photon Dissociation (IRMPD) action spectroscopy. The NH···N stretching vibration between the two ring nitrogens exhibits a frequency of 1570 cm(-1), as confirmed by examination of the proton-bound homodimers of 5-fluoro-1-methycytosine, 2, and of 1,5-dimethylcytosine, 3, which display absorptions in the same region that disappear upon deuterium substitution. (13)C, and (15)N NMR of the solid iodide salt of 1 confirm the nonequivalence of the two rings in the anhydrous proton-bound homodimer at room temperature. IRMPD spectra of the three possible heterodimers also show NH···N stretches in the same domain, and at least one of the heterodimers, the proton-bound dimer of 1,5-dimethylcytosine with 1-methylcytosine, exhibits two bands suggestive of the presence of two tautomers close in energy.
authors.affiliation: Department of Chemistry, University of California, Riverside, CA 92521-0403, USA. morton@citrus.ucr.edu.
authors.forename: Hou U
authors.initials: HU
authors.lastname: Ung
authors.forename: Aaron R
authors.initials: AR
authors.lastname: Moehlig
authors.forename: Ryan A
authors.initials: RA
authors.lastname: Kudla
authors.forename: Leonard J
authors.initials: LJ
authors.lastname: Mueller
authors.forename: Jos
authors.initials: J
authors.lastname: Oomens
authors.forename: Giel
authors.initials: G
authors.lastname: Berden
authors.forename: Thomas Hellman
authors.initials: TH
authors.lastname: Morton
mesh_terms: D003596:Cytosine / Q000031:analogs & derivatives* / Q000737:chemistry; D019281:Dimerization; D005740:Gases / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D011522:Protons; D013055:Spectrophotometry, Infrared; D013696:Temperature
chemical_list: D005740:Gases; D011522:Protons; C031532:1-methylcytosine; D003596:Cytosine